The Weed Resistance Action Group (WRAG)

This web page hosts the latest guidance from the Weed Resistance Action Group (WRAG). The 'Download' button provides background. Scroll down for guidance.

The AHDB-supported Resistance Action Groups (RAGs) are informal, UK-based groups consisting of experts from the Crop Protection Association (CPA) member companies, other representatives from the agrochemical industry, a range of independent organisations, including public-sector research institutes, and the Chemicals Regulation Directorate (CRD).

The groups are completely independent of AHDB and work to produce guidance on pesticide resistance issues. As part of its support to the resistance action groups, AHDB publishes their guidance.


Resistance status


  • Outlooks on Pest Management glyphosate special (December 2018). This issue features several key articles on glyphosate. It includes a paper by James Clarke, chairman of WRAG, which looks at the role of glyphosate and issues around protecting its efficacy.

Resistance testing

Seeing the big picture on herbicide resistance

Seeing the big picture on herbicide resistance

An article from Crop Production Magazine

In this video (above), AHDB's Paul Gosling describes the findings from AHDB research that investigates how farming practices can alter the risk of glyphosate resistance developing in UK grassweeds.


Reports: Black-grass (mainly)

Reports: Other grasses

Reports: Broad-leaved weeds

Herbicide Mode of Action Classification

To find a herbicide's mode of action group, use the Herbicide Resistance Action Committee (HRAC) Mode of Action Classification Map.
HRAC Mode of Action Classification 2020 Map

From 2020, the classification system aligns with the system used by the Weed Science Society of America (WSSA).

This list shows the current groups (with pre-2020 legacy HRAC codes in brackets).

  • 1 (A) Inhibition of ACCase
  • 2 (B) Inhibition of ALS
  • 3 (K1) Inhibition of microtubule assembly
  • 4 (O) Auxin mimics
  • 5 (C1,2) Inhibition of photosynthesis: PS ll – Serine 264
  • 6 (C3)Inhibition of photosynthesis: PS ll – Histidine 215
  • 9 (G) Inhibition of EPSP synthase
  • 10 (H) Inhibition of glutamine synthetase
  • 12 (F1) Inhibition of PDS
  • 13 (F4) Inhibition of DOXP synthase
  • 14 (E) Inhibition of PPO
  • 15 (K3) Inhibition of VLCFAs
  • 18 (I) DHP inhibition
  • 19 (P) Auxin transport inhibitors
  • 22 (D) PS l electron diversion
  • 23 (K2) Inhibition of microtubule organization
  • 24 (M) Uncouplers
  • 27 (F2) Inhibition of HPPD
  • 29 (L) Inhibition of cellulose synthesis
  • 30 (Q) Inhibition of fatty acid thioesterase
  • 31 (R) Inhibition of serine threonine protein phosphatase
  • 32 (S) Inhibition of solanesyl diphosphate synthase
  • 33 (T) Inhibition of homogentisate solanesyltransferase
  • 34 (F3) Inhibition of lycopene cyclase
  • 0 (Z) Unknown mode of action